Organic semiconductor materials are organic substances having the properties of semiconductors. There are known various organic semiconductor materials and organic charge-transfer materials, including: organic low-molecular compounds such as pentacene, anthracene, tetracene and phthalocyanine; polyacetylene-based conductive polymers; polyphenylene-based conductive polymers such as polyparaphenylene and derivatives thereof, polyphenylene vinylene and derivatives thereof and the like; heterocyclic conductive polymers such as polypyrrole and derivatives thereof, polythiophene and derivatives thereof, polyfuran and derivatives thereof and the like; and ionic conductive polymers such as polyaniline and derivatives thereof. In particular, some organic semiconductor materials e.g. organic low-molecular semiconductor and polythiophene can be applied as films to organic substrates e.g. organic polymer substrates by wet processes. It is feasible to manufacture flexible organic electrochromic displays by processing such organic semiconductor films into semiconductor circuits on the organic substrate materials.
The manufacturing of semiconductor elements involves fine processing (sometimes referred to as “pattern processing”) of semiconductor films into desired semiconductor circuits. At this time, coating films are applied to protect the semiconductor films during the fine processing or to protect the circuit patterns after the fine processing.
It is often the case to process the semiconductor film into a circuit pattern by means of a photolithography process. The photolithography process is a technique to apply a photosensitive material (called “resist”) to a substrate, exposing the resist-coated substrate through a photomask or reticle and form a pattern of exposed and unexposed resist regions. The semiconductor film is processed into a circuit pattern by forming a resist pattern through exposure and development of the resist film, and then, dry-etching or wet-etching the semiconductor film.
In the manufacturing of the organic semiconductor element, it is conceivable to form a pattern on the organic semiconductor film by a print process such as relief printing, intaglio printing, planographic printing or screen printing or an imprint process in place of the photolithography process and etch the organic semiconductor film through the pattern. Herein, the imprint process is a technique to apply a coating film to a substrate, allowing a die having a fine pattern of projections and depressions to be pressed against the coating film and thereby transfer the pattern of the die to the coating film.
During the pattern processing of the organic semiconductor film by wet etching, a coating film is applied to the organic semiconductor film such that the organic semiconductor film can be protected from an etchant solvent. It is required that a film-forming composition for forming such a protection film satisfies two important conditions. The first condition is that the film-forming composition is soluble in a solvent that does not cause dissolution or swelling of the organic semiconductor film and thus can be applied to the organic semiconductor film by a wet process. The second condition is that, during the pattern processing of the organic semiconductor film, the wet-coating film can protect the organic semiconductor film from etching. However, it has been difficult to obtain film-forming composition satisfying both of these two conditions.
There are two etching processes: one is a dry etching process using plasma irradiation in a vacuum device; and the other is a wet etching process using a solvent as an etchant. The wet etching process is convenient for etching of the organic semiconductor film because the organic semiconductor film is soluble in the etchant. In general, the organic semiconductor film has an aromatic ring group or heterocyclic group in its structure and can readily be dissolved in an aromatic solvent such as benzene, toluene and xylene.
For example, Patent Documents 1 and 2 disclose film-forming compositions and films formed therefrom such that the films have high etchant resistance and remain unaffected by etchants during the etching of organic semiconductor films into semiconductor circuit patterns.
More specifically, Patent Document 1 discloses a method for manufacturing an organic semiconductor element with stable electrical characteristics and an organic semiconductor element manufactured thereby, wherein, during the manufacturing of the organic semiconductor element, a coating film is formed on an organic semiconductor film by the application of a liquid film-forming composition containing at least one organic solvent selected from propylene carbonate, acetonitrile and dimethyl sulfoxide and an organic compound soluble in the organic solvent.
Patent Document 2 discloses a photosensitive resin composition for forming a coating film with high photoreactivity, good patterning property, high hydrophobicity and good dielectric characteristics, a thin film formed therefrom and a pattern formation method thereof, wherein the photosensitive resin composition contains a solvent such as alcohol, hydrocarbon, halogenated hydrocarbon, ether, ester, ketone, cellosolve, carbitol, glycol ether ester, amide, sulfoxide or nitrile.
However, it can hardly be said that the organic solvent of the film-forming composition of Patent Document 1 and the solvent of the photosensitive resin composition of Patent Document 2 do not affect organic semiconductor films. There has thus been a demand for a film-forming composition and a film formed therefrom that can be applied to an organic semiconductor film, without affecting the organic semiconductor film, and can be patterned by e.g. a photolithography process or imprint process.
Furthermore, Patent Document 3 discloses a positive resist composition for use by exposure to vacuum ultraviolet laser radiation, comprising: an acrylic resin capable of changing its solubility in an alkaline aqueous solution by the action of an acid; and an acid generator, wherein the acrylic resin contains a polymer having an acrylic ester or methacrylic ester moiety with a fluorine-containing ester group.
Patent Document 4 discloses a positive resist composition for use by exposure to vacuum ultraviolet laser radiation of 1 nm to 190 nm wavelength, comprising: an acrylic resin capable of changing its solubility in an alkaline aqueous solution by the action of an acid; and an acid generator, wherein the acrylic resin has a unit obtained by polymerization of fluoroalkyl methacrylate.